Circadian clock and ecophysiological traits in Brassica rapa

Selection during domestication can result in dramatic changes in morphology. Brassica rapa (Brassicaceae) shows morphological differentiation as a consequence of domestication, with the evolution of leafy vegetable crops (subspp. pekinensis and chinensis), root vegetable crops with enlarged below-ground storage structures (subspp. ssp. rapa or rapifera), and oilseed crops with high seed allocation (subspp. oleifera).

Crop selection often leads to dramatic morphological diversification, in which allocation to the harvestable component increases. Shifts in allocation are predicted to impact (as well as rely on) physiological traits; yet, little is known about the evolution of gas exchange and related anatomical features during crop diversification.

In Brassica rapa, we tested for physiological differentiation among three crop morphotypes (leaf, turnip, and oilseed) and for correlated evolution of circadian, gas exchange, and pheno- logical traits. We also examined internal and surficial leaf anatomical features and biochemical limits to photosynthesis.

Brassica crop diversification involves correlated evolution of circadian and physiological traits, which is potentially relevant to understanding mechanistic targets for crop improvement.

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Circadian clock and ecophysiological traits in Arabidopsis thaliana

The circadian clock is a time-keeping mechanism that enables organisms to match physiological, developmental, biochemical and transcriptomic processes with the natural environment.

Circadian rhythms that are closer to 24 hours enhance diurnal timing of gas exchange; it has been also shown that quantitative variation in circadian clock is associated with gas-exchange traits in segregating progenies of Brassica rapa.

Non-photochemical quenching of chlorophyll fluorescence (NPQ) is one protective mechanism by which plants dissipate excessive energy as heat. The process of non-photochemical quenching regulates and protects photosynthetic machinery when the light supply exceeds the light demand. NPQ includes three major components: qE (energy transition quenching), qT (transitory quenching), qI (photoinhibitory quenching).

Our findings suggest that (1) there is a genotypic variation for heat dissipation and (2) there might be coordinated circadian regulation of photochemical and non-photochemical processes under light stress.


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